This invention relates to stratified charge internal combustion engines and particularly to such engines wherein an auxiliary combustion chamber is formed by an insert within the cylinder head.
One prior art auxiliary combustion chamber for an internal combustion engine is shown in published German patent application No. 2,327,703. The auxiliary chamber disclosed in that application is formed using an insert which is placed within the cylinder head from outside of the main combustion chamber. The auxiliary combustion chamber is retained within the cylinder head together with an auxiliary fuel inlet valve which controls the supply of a rich fuel mixture to the auxiliary chamber. The auxiliary chamber has an opening at the end opposite the valve which communicates with a passage through the cylinder head to the main combustion chamber. The auxiliary chamber is secured within a recess in the cylinder head in such a way as to provide a clearance between the interior wall of the cylinder head recess and the outside of the insert forming the combustion chamber. This clearance provides a measure of heat insulation for the auxiliary combustion chamber, thereby enabling the auxiliary combustion chamber to rapidly warm-up. After the auxiliary combustion chamber has reached its normal, elevated operating temperature, the expansion of the insert which forms the auxiliary chamber brings the chamber into close fitting contact with the interior wall of the recess in the cylinder head, thereby enabling more effective transfer of heat from the auxiliary combustion chamber to the surrounding cylinder head.
One problem with prior art auxiliary combustion chambers as described in the published German application is that insertion of the auxiliary combustion chamber from the outside of the cylinder head requires rather complex structural arrangements to maintain the auxiliary combustion chamber within the cylinder head recess. This retaining structure is complicated by the fact that there must be included the auxiliary inlet valve in conjunction with the retaining structure. Another problem with such prior art auxiliary combustion chamber construction is that in the arrangement shown it is possible, prior to full expansion of the insert, that combustion residues, such as carbon, that are formed during engine warm-up, may become embedded between the auxiliary combustion chamber insert and the interior wall of the cylinder head. In this event it will not be possible for the auxiliary combustion chamber insert to come into effective thermal conducting contact with the interior wall of the cylinder head recess. Another problem with the previously disclosed construction is that, because the auxiliary combustion chamber insert is inserted into the cylinder head recess from the side away from the main combustion chamber, and the seat provided for the auxiliary combustion chamber is located toward the outside of the main combustion chamber, the auxiliary combustion chamber, even absent carbon deposits does not come into effective heat transmitting contact with the cylinder head in the region of the passage to the main combustion chamber. This region is the location at which maximum heat-up of the auxiliary combustion chamber is normally encountered. Such excessive heat build-up at the passage between the auxiliary combustion chamber and the main combustion chamber may result in excess temperatures and consequent spontaneous ignitions thereby causing poor engine operation.
A prior U.S. patent application Ser. No. 632,699 filed Nov. 17, 1975, which is assigned to the same assignee as the present inventon, discloses an auxiliary combustion chamber formed by a cup-shaped insert comprising a thin walled generally tubular shell for use in a stratified charge internal combustion engine wherein fuel is delivered to the auxiliary combustion chamber by a fuel injecting device. The insert in this prior application is formed of relatively thin metal in all regions and the side wall of the insert includes a plurality of regions spacedly arranged from one another and force-fittedly applied against the inner wall of the cavity, one of the regions being located adjacent the bottom of the insert. However, since the walls of the insert in all regions are relatively thin, heat dissipation through the walls of the insert is limited. Therefore it is desirable to provide additional heat dissipation especially in the region of the passage between the auxiliary combustion chamber and the main combustion chamber.